Based on temperature dependent far infrared transmission spectra of YMn2O5 and TbMn2O5 single crystals, we report the observation of electric dipole-active magnetic excitations, or electromagnons, in these multiferroics. Electromagnons are found to be directly responsible for the steplike anomaly of the static dielectric constant at the commensurate--incommensurate magnetic transition and are the origin of the colossal magneto-dielectric effect reported in these multiferroics.

Materials exhibiting low-field magnetoelectric and magnetodielectric (MD) effects are necessary for utilization of these effects in multifunctional devices. Since large magnetic fields (H) or electric fields (E) are required to produce any significant effect in existing single-phase magnetoelectrics, recent efforts have been largely devoted to the investigation of laminates or thin film composites made of piezoelectric and magnetostrictive materials. In this work, we report large MD effect Δε∕ε∼3% at remarkably low fields (H<2kOe) in a single-phase material, terbium iron garnet. Our results suggest a route towards future applications of the MD effect in advanced devices.

Application of a magnetic field offers an incisive opportunity to tune competing interactions in complex materials. Here we probe field-induced changes in the local structure of DyMn2O5 by using magnetoinfrared spectroscopy. The high tunability of the dielectric constant and ferroelectric polarization with field is well documented in the literature, but the lattice response on the microscopic level remains unknown. In this work, we reveal the dynamic nature of the local structural response to field and analyze it in terms of calculated mode displacements and local lattice distortions.

Measurements of ferroelectric polarization and dielectric constant were done on RMn 2 O 5 ͑R =Tb,Dy,Ho͒ with applied hydrostatic pressures of up to 18 kbar. At ambient pressure, distinctive anomalies were observed in the temperature profile of both physical properties at critical temperatures marking the onset of long range antiferromegnetic order ͑T N1 ͒ and ferroelectricity ͑T C1 ͒, as well as at temperatures when anomalous changes in the polarization, dielectric constant, and spin wave commensurability have been previously reported. In particular, the step in the dielectric constant at low temperatures ͑T C2 ͒, associated with both a drop in the ferroelectric polarization and an incommensurate magnetic structure, was shown to be suddenly quenched upon passing an R-dependent critical pressure. This was shown to correlate with the stabilization of the high ferroelectric polarization state, which is coincident with the commensurate magnetic structure. The observation is suggested to be due to a pressure-induced phase transition into a commensurate magnetic structure, as exemplified by the pressure-temperature ͑p-T͒ phase diagrams constructed in this work. The p-T phase diagrams are determined for all three compounds.

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